Abstract
4100 Background: Amplification and/or protein overexpression of HER2 in gastric cancer is a prerequisite to establish an adequate treatment strategy. The European standard defined HER2 positivity by IHC as first evaluation assay followed by ISH in 2+ cases. Gastric tumors are heterogeneous and separate evaluations lead to uncertainties and in localizing distinct clones and are time consuming. The aim of this study was to evaluate the feasibility of gene-protein platform in comparison to single staining methods. Methods: IHC plus SISH and gene-protein platform (IHC/SISH, protein/gene) method for HER2 were performed in randomly collected 100 cases of gastric carcinoma. Results of IHC and SISH were compared with IHC/SISH staining. Rüschoff criteria were applied. Tumors were HER2 positive when expression 3+ or 2+ plus gene amplification (EU-Norm) was found. In Second definition (US-Norm), tumors showing HER2 expression 3+ or amplification were considered HER2 positive. Results: 96 of 100 samples were eligible. Amplification was observed in 14.6% and 15.6% by SISH and IHC/SISH. 71.9% by IHC vs. 75.0% by IHC/SISH had no expression (0) and 10.4% (IHC vs. IHC/SISH) had weak (1+) HER2 expression. Moderate expression (2+) and overexpression (3+) were observed in IHC 6.3%/11.5% and IHC/SISH 6.3%/8.3%, respectively. There were high concordances in IHC assessment of cases with score 0 (94.8%; κ=0.87) and 3+ (96.9%; κ=0.83) and moderate concordances in 1+/2+ cases (89.6%; κ= 0.44 vs. 93.8%; κ=0.47). Rate of HER2 positivity was similar in standard or novel method. In EU Definition 14.6% vs. 10.4% (p=0.52) were positive, respectively, with very good concordance (95.8%; κ=0.81).Concordance between HER2 positivity in standard or novel method was very good (99.0%; κ=0.96) in US definition with no significant differences (17.7% vs. 16.7%; p=1). Conclusions: Gene-protein platform has been tested for first time in gastric carcinoma. Results showed that this novel platform can be a feasible alternative to single methods. Discrepancies in cases with weak or moderate HER2 expression can be a result of observer variability.
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